1. Field of the Invention
This invention relates to structures and methods for fabricating magnetic write heads. More specifically, the invention relates to structures and methods for fabricating thin film longitudinal and perpendicular magnetic write heads having layered return poles.
2. Description of the Related Art
FIG. 1 (Prior Art) is a partial cross sectional view of a typical thin film longitudinal head, wherein write gap 112 is bounded by upper 110 and lower 108 pole tips. Upper pole tip 110 is in contact with upper return pole layer 114. Lower pole tip 108 is in contact with lower return pole layer 106. Lower return pole layer is separated from shield layer 102 by insulating layer 104. The coil is shown as structure 116.
Typically, layered pole structures (structures with alternating layers of different compositions of materials) in prior art longitudinal write heads have been limited to upper pole tip 110 and lower pole tip 108, as disclosed, for example in US Patent Application Publication 2003/0048582, FIG. 3. Return pole layers (106, 114) have been generally comprised of a magnetic alloy of uniform composition, for example 45% Ni, 55% Fe. Dinan et al., U.S. Pat. No. 6,912,771, discloses upper and lower return poles having a graduated Fe concentration varying from about 20 atomic % to about 55-65 atomic %. However, unlike the embodiment disclosed in FIG. 1, there are no distinct pole tips 110, 108 disclosed in Dinan, as the return poles extend to the ABS and have the write gap directly between them. Dinan does not disclose any improved head performance, except to point out that the graduated Fe concentration can be produced in a single electroplating bath, reducing fabrication costs.
FIG. 2 (Prior Art) is a partial, cross sectional view of a thin film perpendicular write head 200. The head comprises shield layers 202, 204, shaping layer 210, coil structure 208, main pole 212, lower return pole layer 206, wrap around shield 214, and upper return pole layer 216. Alternatively, structure 214 may also be a trailing shield. Details of wrap around shields and trailing shields, as applied to perpendicular recording heads, can be found in, for example, US Patent Application Publications 2007/0146930, 2007/0115584, 2006/0174474, 2006/0044682, and 2007/0137027. Typically, lower return pole layer 206 and upper return pole layer 216 are composed of a magnetic material of uniform composition. Layered structures, comprising alternating layers of different compositions, have yet be employed in upper and lower return poles in perpendicular heads of the prior art.
While thin film write heads of the prior art can provide adequate performance, what is needed is a better write head structure that can provide higher efficiency and lower noise for both longitudinal and perpendicular heads.
United States Patent Application Publication 2003/0048582 discloses an upper magnetic pole layer and/or lower magnetic pole layer comprising a soft magnetic film having a variable region in which the chemical composition of Fe changes in the direction of thickness in at least a part thereof, and the difference of the proportions of Fe between the regions most abundant in Fe and most deficient in Fe is 4% by mass or more in the variable region. The structure of the soft magnetic film permits the saturation magnetic flux density Bs to be improved while decreasing the coercive force Hc by forming fine crystal grains, thereby enabling a thin film magnetic head excellent in high density recording to be manufactured.
U.S. Pat. No. 6,912,771 discloses a magnetic head for a hard disk drive. The magnetic poles of the head are formed with a NiFe alloy having a graduated composition in which a higher Fe concentration is fabricated proximate the write gap layer between the magnetic poles. Each magnetic pole is fabricated in a single electroplating step in which the duty cycle of the electroplating current is altered during the electroplating operation. Where the duty cycle is greatest the Fe ion concentration is likewise greatest.
U.S. Pat. No. 6,794,063 discloses a thin film magnetic head having sufficient recording performance on a recording medium imparted with a large coercive force. A plated magnetic thin film can be obtained in which a crystal grain size is modulated in a film thickness direction and a coercive force is reduced. Further, even for a composition area indicating a high saturation magnetic flux density in which, conventionally, soft magnetic properties could not be obtained, a magnetic film having an excellent soft magnetic property can be manufactured.
U.S. Pat. No. 4,279,707 discloses that electroplating nickel-iron alloys onto objects having complex topographical shapes with projections and hollows such as upper pole pieces of thin film magnetic recording heads has been found to yield a substantial variation in nickel-iron alloy composition from point to point within a single pattern. Providing a low total dischargeable ion concentration in the bath is helpful to reduce such variations when plating in the 80:20 Ni:Fe alloy range.
U.S. Pat. No. 4,242,710 discloses a thin film inductive head formed with nickel-iron binary alloy or nickel-iron-X ternary alloy pole pieces characterized by negative magnetostriction having a saturation magnetostriction coefficient in the range of 1×10−6 to 5×10−6.